1. Field of the Invention
This invention relates to compositions including copolymers containing sulfur which contain both silicon-free organic segments and organosilicon segments. This invention also relates to compositions including mixtures of at least two different types of components selected from the following three types: the above copolymers, silicon-free organic compounds containing sulfur and/or organosilicon compounds containing sulfur. This invention also relates to a method of forming higher molecular weight products from the above compositions. This invention further relates to organic-organosilicon compound gels, gums, resins and elastomers containing sulfur.
2. Description of the Prior Art
Compositions consisting of mercapto-functional copolymers which contain both silicon-free organic segments and organosilicon segments which are free of aliphatic unsaturation such as vinyl and are polymerized or cured by means of the mercapto groups are known in the art. Many types of curing or condensing agents have been suggested such as inorganic peroxides such as sodium peroxide or lead peroxide; inorganic oxidizing agents such as chromate or permanganate salts; organic peroxides such as benzoyl peroxide; organic hydroperoxides such as cumene hydroperoxide and other organic curing agents such as polyepoxides, polyisocyanates or oximes and the like, many of which are detailed in Canadian Pat. Nos. 783,649 and 911,098
Vanderlinde, in U.S. Pat. No. 3,445,419, teaches the production of a type of mercapto-functional copolymer consisting of organosiloxanes with mercapto-functional organic compound segments which are prepared by grafting a mercapto-functional carboxylic acid ester such as pentaerythritol tetrakis(3-mercaptopropionate) onto a vinyl-terminated organosiloxane. When an alkaline catalyst such as an amine is added to the resulting graft-copolymer, there is obtained a composition which is stable in the absence of air, but cures to an elastomer at room temperature upon exposure to air.
Curable mixtures of mercapto-functional organic polymers and mercapto-functional organosiloxanes, free of aliphatic unsaturation, are known as exemplified by Pines, et al. in Canadian Pat. No. 907,436. Pines, et al., above; Giordano in U.S. Pat. No. 3,312,669 and British Pat. No. 1,279,475 teach curable mixtures of mercapto-functional organic polymers and organosilanes. None of the above patents suggest the use of iron carbonyl compounds as catalysts nor do they suggest that the acids hereinafter described can be used to accelerate the surface polymerization or cure of such compositions.
Nametkin, et al., in the Journal of Organometallic Chemistry, 149, pp. 355-370 (1978) report that when stoichiometric amounts of Fe(CO).sub.5, Fe.sub.2 (CO).sub.9 or Fe.sub.3 (CO).sub.12 are reacted with thiols of the general formula RSH, where R is an alkyl or aryl radical, in solution, a complex {RSFe(CO).sub.3 }.sub.2 and a small amount of the disulfide, RSSR, is produced at room temperature and that Fe.sub.3 (CO).sub.12 is the most effective catalyst. Thermal decomposition of the complex in n-dodecane solution at 160.degree. C. in the presence of air results in decomposition of the complex to form the disulfide. However, this article does not teach that Fe(CO).sub.5, Fe.sub.2 (CO).sub.9 or Fe.sub.3 (CO).sub.12 will function as a catalyst in non-stoichiometric amounts for the room temperature polymerization or cure of the compositions hereinafter described nor does it suggest that the acids hereinafter described will accelerate the surface reaction of such compositions.
Gary R. Homan and Chi-Long Lee are the applicants named in United States Patent Application Ser. No. 99,254, filed on Dec. 3, 1979, entitled "Oxygen Curable Mercapto-Functional Organosilicon-Organic Compound Compositions Catalyzed By Metal Carbonyl Compounds And Method Of Forming Higher Molecular Weight Products Therefrom" which is assigned to the same assignee as is the present invention. In that patent application, Homan and Lee teach that metal carbonyl compounds, especially those containing iron, can be employed as polymerization or cure catalysts in compositions which include (a.) mercapto-functional copolymers which contain both silicon-free organic compound segments and organosilicon segments, or mixtures of (b.) silicon-free mercapto-functional organic compounds and (c.) mercapto-functional organosilicon compounds. Other useful compositions can be prepared from mixtures of at least two different types of components selected from a, b, or c, above. When catalyzed mixtures are prepared and stored in the substantial absence of oxygen, storage-stable compositions which polymerize or cure at room temperature upon exposure to oxygen can be obtained. The products formed upon exposure to oxygen are useful in a variety of applications, for example, as coatings, encapsulating gels, or elastomeric sealants. By varying the ratios of silicon-free organic compounds or segments to organosilicon compounds of segments in the mixtures or copolymers, the properties of the resulting products can be altered to suit the desired end-use.
The advantages of employing organosiloxanes in place of organic polymers are well-known. For example, organosiloxane elastomers are known to be flexible at much lower temperatures than are organic elastomers. Thus, organosiloxanes can be included in organic elastomer formulations to bring about an improvement in the low temperature flexibility of the cured elastomer. Such mercapto-functional compositions are readily cured by means of the metal carbonyl compound catalysts of the present invention simply by exposing the composition to atmospheric oxygen.
Quite unexpectedly, it was discovered that when an acid which satisfies the criteria set out below was included in iron carbonyl catalyzed compositions taught by Homan and Lee, above, the composition exhibited a much faster rate of surface polymerization or cure than did the same compositions without such an acid. Compositions containing such an acid are especially useful where thin films are coated on articles such as wire, paper or electronic circuit boards because the rapid surface cure at room temperature enables the articles to be handled at a much earlier time than compositions which do not contain acid accelerators. Rapid surface cure also reduces the amount of time the surface is tacky and thus vulnerable to contamination by dust or other foreign matter.